As an increasing number of computer users install wireless networks that meet the Institute of Electrical and Electronics Engineers (IEEE) 802.11 specifications in their homes and workplaces, it has become apparent that the performance (i.e., range and data rate) of such systems often fails to meet their expectations. Structures built of stone or brick, or which contain blocking interior elements, such as a fireplace, mirror, refrigerator, or other large metal or masonry furnishings, often cause problems in achieving adequate RF coverage at a desired data throughput. Throughput can be very important when the signal being conveyed is streaming video or other multimedia signal that cannot be interrupted or delayed without readily discernible adverse effects. The actual data rate that can be achieved quickly decreases as the distance between wireless communication devices and other factors reduce the received signal strength of the wireless transmissions. Also, the reception at a client device can be disrupted as a person or other object moves through the signal path to the access point, or if the client device, which is often a laptop or other portable computing device, moves even a few centimeters. Wireless devices attempt to minimize the effects of such disturbances to the signal path by using two antennas and a diversity switch that is controlled to automatically select the antenna providing the better signal strength, but on a laptop wireless card, the two antennas are only 2-3 cm apart, so the benefit is not as great for more significant disruptions in the signal path.
Existing IEEE 802.11 technologies retransmit data packets to compensate for signal fades that cause data packets to be corrupted or dropped during transmission. Packet retransmission is not particularly evident to users when they perform batched operations, such as browsing web pages. A page that loads two seconds slower or faster on a wireless laptop, depending upon radio conditions and/or signal strength, is typically not evident to users. In contrast, users are cognizant and intolerant of pauses in a streaming audio or video feed that occur while the system attempts retransmission. Consequently, software designers of systems that use wireless links often provide megabyte-sized jitter buffers to temporarily hold data for retransmission/reception in an attempt to prevent noticeable pauses or dropouts. However, these buffers cause a lag in the media data feed (latency), increase memory requirements, and generally make a wireless system more complex than is necessary.
Frequently, the only way to achieve a desired coverage and throughput in an office or home is to add more access points so that the distance and/or intervening structural elements between the access points and the clients devices are reduced, which means higher wiring costs to run Ethernet cabling to the additional access points and greater equipment costs for each added access point. Increasing transmitter power is typically not an option due to regulatory limitations and/or because significantly increased power consumption is not acceptable for a battery powered side of a link. As an alternative to adding more access points, significant performance improvements might be achieved by providing any existing access point and/or client device with the ability to focus RF energy in an appropriate direction, so that the energy is only transmitted or received in the direction required, rather than being directed or received by one of the more conventional dual omnidirectional antennas used on most commercially available wireless access points and client devices.
The benefits of controlling RF energy with a directional antenna in this manner are well known. However, the direction in which the RF energy needs to be transmitted or received is not fixed in most wireless systems, because a fixed access point must be able to maintain communications with moving client devices, or communicate with client devices that are located at different positions scattered around the access point. A fixed directional antenna is therefore only an acceptable solution to improve the gain of the wireless communication signal in systems where the devices communicating with an access point or with each other are fixed and the link between the devices is limited to the fixed direction. Alternatively, some commercial systems will use a plurality of wireless transceivers, each coupled to a different directional antenna that is directed toward a fixed wireless device. Such systems are generally too costly for home or small business use, however.
Electronically and mechanically steerable antennas have been used for decades in military and industrial applications to improve the range of radio communications links and the range of radar systems. Unfortunately, these systems are typically large and very expensive, and consequently, have generally not appeared in consumer products. More recently, electronically steerable antenna technology has been used at cellular telephone network base stations to improve channel capacity and range. This technology is also beginning to appear in commercial access points intended for installation in large scale commercial applications, such as at airports or in universities, but suitable systems still cost thousands of dollars. A multi-sector antenna is another form of steerable antenna and includes a plurality of sectors, each of which can transmit and receive in a different direction, i.e., perpendicular to the face of the sector.
Clearly, a more affordable approach is needed that can provide most of the benefits of these more expensive and complex systems that have been developed for steering an antenna, but at a reasonable cost level that is acceptable for consumer products of this type. Such a product should control selective switching of the antenna beam direction as needed to maintain the best communication link. For example, a client device provided with a relatively low cost multi-sector antenna or other steerable antenna should be able to control the antenna to achieve a much higher data rate when communicating with an access point, by selecting the best direction of the steerable antenna for the communication link. The best or preferred direction can change due to changes in the signal path, so it would be desirable to automatically detect when any deterioration of the signal has occurred and automatically select a new preferred direction for the communication link.